feat: VK OAuth flow, catalog sync improvements, and expanded test suite

- Add VK OAuth implicit flow: /vk-auth redirect, /vk-callback JS page,
  /vk-callback/save endpoint with state validation
- Add VK_CLIENT_ID/VK_CLIENT_SECRET to config
- Add refresh_token/token_expires_at columns to vk_connections (migration 0006)
- Fix vk_catalog task: handle price/thumb_photo as string or dict (VK API v5.199)
- Fix connections/vk/test: use groups.getById instead of market.getAlbums
  (works with both user and group tokens)
- Add orphan deletion to mirror_to_vk: VK products not in Evotor are removed
- Handle ungrouped Evotor products: push to "Без категории" VK album
- Respect SyncConfig.is_enabled in mirror_to_vk
- Add product count column to catalog groups page
- Add group name column to catalog products page
- Expand test suite: 73 new tests covering connections routes, catalog routes,
  vk_sync task logic, and catalog task helpers (138 total, all passing)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/routes/catalog.py

@@ -2,6 +2,7 @@ from datetime import datetime, timezone
 
 from fastapi import APIRouter, Depends, Request
 from fastapi.responses import HTMLResponse, RedirectResponse
+from sqlalchemy import func
 from sqlalchemy.orm import Session
 
 from web.auth.session import get_current_user
@@ -99,9 +100,19 @@ async def catalog_groups(store_evotor_id: str, request: Request, db: Session = D
         .all()
     )
     enabled_ids = _enabled_group_ids(db, user.id, store_evotor_id)
+
+    counts_q = (
+        db.query(CachedProduct.group_evotor_id, func.count().label("cnt"))
+        .filter(CachedProduct.user_id == user.id, CachedProduct.store_evotor_id == store_evotor_id)
+        .group_by(CachedProduct.group_evotor_id)
+        .all()
+    )
+    product_counts = {row.group_evotor_id: row.cnt for row in counts_q}
+
     return _render(request, "catalog/groups.html", {
         "user": user, "store": store, "groups": groups,
         "enabled_ids": enabled_ids,
+        "product_counts": product_counts,
     })
 
 
@@ -135,12 +146,14 @@ async def catalog_products(store_evotor_id: str, request: Request, db: Session =
         .order_by(CachedGroup.name)
         .all()
     )
+    group_map = {g.evotor_id: g.name for g in groups}
     return _render(request, "catalog/products.html", {
         "user": user,
         "store": store,
         "products": products,
         "groups": groups,
         "group_id": group_id,
+        "group_map": group_map,
     })